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Did yours have an accumulator as well? If you read further on, you will understand why I am asking.

UPDATE:
So, the oil cooling loop had a leak at one of the couplings we put in. The old copper tubing wasn't playing very nice with the Sta-Brite. We got it fixed, put in a new Drier/Filter (SUD111) and hooked up the vacuum pump for about 5 hours. I wasn't going to let any moisture sneak by this time.

I had one last 14 ounce can of R12. The new drier was slightly longer and larger than the stock one, so we put most of the can in. We did not have a way to measure our charge so we are left to do superheat / subcooling / pressure checks.

This thing has no problem going down 2"mg on the suction (as the freezer gets down to the -5*F mark) and the head pressure is around 130 psi. The strainer is pretty warm still but the suction line is sweating since it is pretty cold (around 50*F the last time I checked).

Is it normal for these things to sweat like that? My R134 fridge has a relatively warm suction line.

So, since this freezer has the condenser located inside the shell of the freezer, I have no access to the suction line as it exits the accumulator/evaporator. However, the cap tube and suction line are soldered together as they just enter the shell and go inside. About 18 inches away, I have an access hole I made to leak check and I can see the suction line/cap tube are frosted up pretty good.

Is this a sign that I am overcharged? Since I have an accumulator, should I not have any frost inside where the cap tube and suction tube are connected? Or is this a normal situation, where the cap tube and suction line are frosted, but not within 18 inches (or further) from the compressor?

If I am to read superheat at the suction line (6inches from the compressor), what's a good number?

Took superheat at the inlet of the compressor. I do believe they run the liquid cap tube together to get extra subcool.
Mine freezes all the way to the compressor but is not flooding.
Mine does not have an accumulator but it would be a good idea.

The thermostat was also shot. I purchased one of those temperature controllers (10A rated) for cooling/heating. It included a thermistor which I installed where the old dial was located on the inside of the freezer (middle shelf on the wall). Thing is pretty neat. Totally programmable.

The one that controls the AC in your house or the one used in a walk-in is a direct control thermostat. The thing that cycles the compressor in a freezer like yours is called a cold control. It's important to distinguish one from a thermostat since the behavior is quite different. It uses an indirect method to control box temperature as a part of an engineered product.

That controller doesn't even look UL listed, quacks like CHINA MADE and smells like China QC.
I would try ditching that China made microcontroller based embedded wreckthems driven BS and use a real electromechanical freezer cold control installed in the same way the original one was installed. If the original was in zigzag or coiled, the replacement needs to be setup like it too.

The location, orientation and shape of the sensory tube affects the integration behavior and affects the box temperature especially in passive convection evaporator type. Cold control is not a single point sensing. It senses across the entire length.

After a day, I changed the temperature settings to -5F to +5F, a 10 degree swing. The unit would run for 91 minutes, and be off for 90 minutes. I put more food into the freezer to help maintain the colder temperatures.

After a day or so, the unit seemed to struggle more. It would run for 90 minutes to hit -5F, and be off for 45 minutes to hit +5. It appears that the more load in the freezer, the more it struggled to reach these lower temperatures.

It almost seems like the location or shape of the sensor is wrong. A recovery time that long suggests the sensor is thermally too heavy, or that junk controller is messing everything through its Chinese Poorly Implemented Disarray algorithm that's not appropriate for a small freezer.

How are you measuring the temperature? You'd want to freeze a probe into a place in meat or inside a bag of corn to get a better idea of average (integrated) box temperature, but the sensing tube should be very rapidly responding. Thermistor is generally quite slow to respond and can cause excess integration to occur and cause swinging in temperature of stuff inside the freezer.

I would try ditching that China made microcontroller based embedded wreckthems driven BS and use a real electromechanical freezer cold control installed in the same way the original one was installed. If the original was in zigzag or coiled, the replacement needs to be setup like it too.

The original cold control was routed inside the aluminum walls of the freezer. I can not and will not be able to find the original routing or the final location of the bulb (whether it was on or near the evaporator).

Originally Posted by ICanHas

The location, orientation and shape of the sensory tube affects the integration behavior and affects the box temperature especially in passive convection evaporator type. Cold control is not a single point sensing. It senses across the entire length.

I wish I could have seen the original routing of the sensory tube so I could rig this thing up properly.

Originally Posted by ICanHas

How are you measuring the temperature? You'd want to freeze a probe into a place in meat or inside a bag of corn to get a better idea of average (integrated) box temperature, but the sensing tube should be very rapidly responding.

Fortunately, this thermistor has a rapid response. When the door is opened, the temperature on the display responds almost immediately and updates every two to three seconds accordingly. I like your idea of freezing it into a bag of corn or something similar to get a better average temperature. The thermistor is sticking past the wall about three inches. I was hoping this location would help it get air temperature, and not the wall temperature. It may just be too close to the door and is reacting to the heat gain/loss through the old insulation.

I'm still in the process of trying to find the sweet spot for the refrigerant charge. I feel that I am still slightly overcharged, but I do not want to go under since I am all out of R12.

On my upright, the sensing line is attached on the bottom side of second from top shelf/evaporator. It's not touching, but suspended under a small plastic spacer so it's not actually touching the evaporator coil. Refrigerant enters at the top, then suction at the bottom. It's in the center horizontally, then towards the back.

Maybe try that position. You got me curious, so I got data logging going last night. I"ll post it later.

The only right charge is the nameplate charge. If you're having to add beyond your filter drier size difference, it means your cap tube is restricted.

Here's what it looks like with a very fast responding thermocouple where the cold control is:

The bottom one is from a different time. Temperature setting might have been different, but the cold control differential is the same. I used a sensor that was much heavier thermally.
As you can see, there's quite a difference in swing as seen by the sensor depending on sensor's thermal mass.

I logged the resistance of one of the eart buds of 16 or 32 ohm earphones from the dollar store as a copper RTD since copper is pretty much linear. The unit is in °C, because, the equation was more readily available. That huge spike is from when the door was opened.

On my upright, the sensing line is attached on the bottom side of second from top shelf/evaporator. It's not touching, but suspended under a small plastic spacer so it's not actually touching the evaporator coil. Refrigerant enters at the top, then suction at the bottom. It's in the center horizontally, then towards the back.

You, sir, are a gentleman!! Thank you so much for this information. I don't have a way to connect it in that exact spot, but I did get the probe right next to the evaporator at the back left corner. I need to find a way to attach this thing (a little difficult with a -5*F freezer).

I think moving this probe to the new location will help greatly! And thank you so much for your temperature/time plot! This is some seriously rock-solid data to work with. Now I can adjust my temperature controller to behave in a much similar way to the original cold control.

I have been reading the SAM manuals, Copeland Manuals, Fridge/Freezer Repair Tech manuals (from the 70s) all trying to find some hard data for temperatures.

With your chart, I can make this POS temperature controller behave in a way that is close to the original settings.

A freezer that old was quite inefficient to begin with even in perfect conditions. If there's anything less than optimal, it only goes down hill. To name a few, degrading insulation, partially clogged capillary, worn compressor, worn gasket and incorrect charge level.

If this is just some crappy old freezer and not some kind of iconic vintage, I'd be careful. Updating semi-modern freezer won't do much, but many from something that old guzzles power. It's not uncommon for something that old to use 1,400 kWh/year... and the cost is whatever your power rate is. At the national average, that's gonna cost you about $170 a year in power or about 3 times what modern ones use.

As much as I dislike a lot of today's China made stuff, 30-40 years is getting to the end of useful life.

Capillary obstruction problems are quite common. I had an R12 freezer. Worked good for a few months. Capillary clogged up, which made it not equalize and preventing compressor from starting. It thawed out. about $200 loss in food and I thought I saw hell taking out the rotting mass inside.

Mine's about half the cu.ft size of yours, quite new, manual defrost, quite new and Energy Star and its doing about 0.85kWh/day.